It is well known that primary hydrocarbon recovery techniques recover only a portion of the petroleum in any formation. Numerous secondary and tertiary recovery techniques have been suggested and employed to increase the recovery of hydrocarbons from the formations where they are located. Thermal recovery techniques have proven to be among the most effective of these techniques in increasing the amount of oil recovered. The primary thermal recovery technique uses steam injected into the formation with the heat generated thereby warming the hydrocarbons to less viscous states wherein the steam head can drive the product through the porous formation to a recovery well. A good description of this can be found in U.S. Pat. No. 4,321,966.
Steamflooding is, however, an expensive operation requiring the use of high capital equipment that is costly to operate. Thus, it is important that the steam generating equipment be used in the most efficient manner.
It is known to steamflood a formation with high quality steam and then allow the quality of steam to taper off. This is fully described in U.S. Pat. No. 4,491,180. A somewhat similar method is described in U.S. Pat. No. 4,495,994, which also includes in situ combustion to conclude the recovery. Other known steamflooding methods include injection of polymers and other materials at some point during the operation. For example, U.S. Pat. No. 4,702,317 describes caustic agents; U.S. Pat. No. 3,853,178 describes an alkali metal hydroxide; and U.S. Pat. No. 4,660,641 describes an alkalinity agent.
All of the foregoing patents relate to recovery of hydrocarbon product from a single layer formation and do not consider problems which may arise in multi-layered formations. While it might be expected that techniques applied to a single layer formation could simply be repeated for each successive formation, this may work, but, also may be very inefficient and therefore be costly.